Current investigations are being conducted on the events leading to the formation of several types of cataracts. Diabetic and galactosemic cataract formation, inhibited by the enzyme aldose reductase, are being studied as well as methods for controlling the onset of these cataracts through the regulation of aldose reductase. The relationship between aldose reductase and other ocular diabetic complications such as retinopathy, corneal epitheliopathy, and basement membrane thickening is also being investigated. Methods for delaying the onset of these complications through the pharmacological control of aldose reductase are also being developed. The potential role of the enzyme pyrroline-5-reductase as well as the pyrroline-5-carboxylate (P-5-C) cycle through which ornithine and glutamine are converted to proline are also being investigated. Pyrroline-5-reductase has been proposed to regulate cellular redox potentials and increase ATP levels through stimulation of the pentose shunt. Cataracts are associated with patients with gyrate atrophy of the choroid and retina, a disease in which high ornithine levels result from the absence of the key enzyme ornithine amino transferase which converts ornithine to pyrroline-5-carboxylate. Hereditary cataract formation is also being studied in a strain of mice developed in our laboratory. These animals, known as Philly mice, develop osmotic cataracts by an as yet unknown mechanism.